Crystals of laquinimod sodium, and process for the manufacture thereof

ABSTRACT

Disclosed is a process for the preparation of laquinimod sodium which removes the impurities after the salt formation step, thus resulting in crystals of higher purity as well as crystals having improved crystalline characteristics.

This application claims the benefit of U.S. Provisional Application No.60/728,657, filed Oct. 19, 2005, the entire contents of which are herebyincorporated by reference.

Throughout this application various publications, published patentapplications, and published patents are referenced. The disclosures ofthese publications in their entireties are hereby incorporated byreference into this application in order to more fully describe thestate of the art to which this invention pertains.

BACKGROUND OF THE INVENTION

Laquinimod is a compound which has been shown to be effective in theacute experimental autoimmune encephalomyelitis (aEAE) model (U.S. Pat.No. 6,077,851). Its chemical name isN-ethyl-N-phenyl-1,2,-dihydro-4-hydroxy-5-chloro-1-methyl-2-oxoquinoline-3-carboxamide,and its Chemical Registry number is 248281-84-7. The processes ofsynthesis of laquinimod and the preparation of its sodium salt aredisclosed in U.S. Pat. No. 6,077,851. An additional process of synthesisof laquinimod is disclosed in U.S. Pat. No. 6,875,869.

In the preparation of laquinimod sodium disclosed in U.S. Pat. No.6,077,851, laquinimod acid was suspended in ethanol, and 5M sodiumhydroxide solution was added. After stirring, the resulting precipitatewas filtered, washed with ethanol, and dried. The method used to makelaquinimod sodium in U.S. Pat. No. 6,077,851 is commonly referred to asa slurry-to-slurry salt formation.

In the slurry-to-slurry salt formation method of laquinimod sodium, thelaquinimod sodium is not dissolved in solution. Any solid impurities, ifpresent in the laquinimod sodium suspension, are therefore not removedby filtration.

Applicants have found that the slurry-to-slurry formation of laquinimodsodium usually results in a product contaminated with other compoundsand/or metals. Disclosed is a process for the preparation of laquinimodsodium which addresses this.

SUMMARY OF THE INVENTION

Disclosed is a process for the preparation of laquinimod sodium whichremoves the impurities present after the salt formation step, thusresulting in crystals of higher purity as well as crystals havingimproved crystalline characteristics.

The subject invention provides a mixture of crystalline laquinimodsodium particles, wherein 10% or more of the total amount by volume ofthe laquinimod sodium particles have a size of greater than 40 microns.

The subject invention also provides a mixture of crystalline laquinimodsodium particles, having a tapped density of at least 0.6 g/mL.

The subject invention also provides a composition comprising laquinimodsodium and no more than 2 ppm of a heavy metal calculated based on thetotal amount of laquinimod sodium in the composition.

The subject invention also provides a process of recrystallization oflaquinimod sodium comprising:

-   -   a) dissolving laquinimod sodium in water to form an aqueous        solution;    -   b) concentrating the aqueous solution to form a concentrated        solution;    -   c) adding a water-miscible anti-solvent to the concentrated        solution to form laquinimod sodium crystals; and    -   d) isolating the laquinimod sodium crystals.

The subject invention also provides a process for making apharmaceutical composition comprising laquinimod sodium comprising:

-   -   a) obtaining a batch of laquinimod sodium;    -   b) determining whether insoluble matter is present in the batch        of step a) by mixing a sample from the batch in deionized water        at room temperature at a ratio of at least 110 mg of sample to        1.0 ml of water, and inspecting the resulting mixture for the        presence of insoluble matter; and    -   c) mixing the batch of step a) with at least one        pharmaceutically acceptable carrier if in step b) insoluble        matter is determined to be present below a predetermined amount.

BRIEF DESCRIPTION OF FIGURES

FIG. 1: Scanning electron micrograph of laquinimod sodium preparedaccording to Example 1 (batch B) from Example 14, beforerecrystallization.

FIG. 2: Scanning electron micrograph of recrystallized crystals fromExample 15.

FIG. 3: Scanning electron micrograph of recrystallized crystals fromExample 16.

DETAILED DESCRIPTION OF THE INVENTION

The subject invention provides a mixture of crystalline laquinimodsodium particles, wherein 10% or more of the total amount by volume ofthe laquinimod sodium particles have a size of greater than 40 microns.

In an embodiment of the mixture, 50% or more of the total amount byvolume of the laquinimod sodium particles have a size of greater than 15microns.

In a further embodiment, the mixture has a tapped density of at least0.6 g/mL, at least 0.5 g/mL, or at least 0.4 g/mL.

In another embodiment, the mixture has a bulk density of at least 0.4g/mL,'at least 0.3 g/mL, or at least 0.2 g/mL.

In yet another embodiment, the mixture has a tapped density of less than0.8 g/mL, or less than 0.7 g/mL.

In a further embodiment, the mixture comprises no more than 2 ppm of aheavy metal. The heavy metal may be iron, nickel or chromium.

In an embodiment, the mixture comprises no more than 2 ppm of iron, nomore than 1.5 ppm of iron, or no more than 1 ppm of iron.

In a further embodiment, the mixture comprises no more than 0.2 ppm ofnickel, no more than 0.15 ppm of nickel, or no more than 0.1 ppm ofnickel.

In yet a further embodiment, the mixture comprises no more than 0.3 ppmof chromium, no more than 0.25 ppm of chromium, no more than 0.2 ppm ofchromium, no more than 0.15 ppm of chromium, or no more than 0.1 ppm ofchromium.

The subject invention also provides a pharmaceutical compositioncomprising any of the disclosed mixtures and a pharmaceuticallyacceptable carrier. The pharmaceutical composition may be in the form ofa tablet or capsule.

The subject invention also provides a composition comprising laquinimodsodium and no more than 2 ppm of a heavy metal calculated based on thetotal amount of laquinimod sodium in the composition. The heavy metalmay be iron, nickel or chromium.

In an embodiment, the iron content of the composition is no more than 2ppm, no more than 1.5 ppm, or no more than 1 ppm.

In a further embodiment of the composition, the nickel content is nomore than 0.2 ppm, no more than 0.15 ppm, or no more than 0.1 ppm.

In yet a further embodiment of the composition, the chromium content isno more than 0.3 ppm, no more than 0.25 ppm, no more than 0.2 ppm, nomore than 0.15 ppm, or no more than 0.1 ppm.

In another embodiment, the composition is in crystalline form. Acomposition in the crystalline form may be in the form of any of thedisclosed embodiments.

The subject invention also provides a process of recrystallization oflaquinimod sodium comprising:

-   -   a) dissolving laquinimod sodium in water to form an aqueous        solution;    -   b) concentrating the aqueous solution to form a concentrated        solution;    -   c) adding a water-miscible anti-solvent to the concentrated        solution to form laquinimod sodium crystals; and    -   d) isolating the laquinimod sodium crystals.

In an embodiment of the process, step a) is performed by heating theaqueous solution to a temperature of 40-80° C.

In a further embodiment of the process, the concentrated solutioncomprises 1-4 milliliters of water per gram of laquinimod sodium.

In a further embodiment of the process, the concentrated solutioncomprises 1-2 milliliters of water per gram of laquinimod sodium.

In another embodiment of the process, the anti-solvent is one, or amixture of more than one, of the group consisting of ethanol,isopropanol, and acetone.

In another embodiment of the process, the anti-solvent is acetone.

In yet another embodiment of the process, the anti-solvent is added inan amount between 3 and 15 milliliters per gram of laquinimod sodium.

In a further embodiment of the process, step c) is followed by coolingthe solution to a temperature of below 10° C.

In yet a further embodiment of the process, step b) is followed byseeding the concentrated solution with laquinimod sodium.

The subject invention also provides laquinimod sodium prepared by anyone of the disclosed processes.

A process for making a pharmaceutical composition comprising laquinimodsodium comprising:

-   -   a) obtaining a batch of laquinimod sodium;    -   b) determining whether insoluble matter is present in the batch        of step a) by mixing a sample from the batch in deionized water        at room temperature at a ratio of at least 110 mg of sample to        1.0 ml of water, and inspecting the resulting mixture for the        presence of insoluble matter; and    -   c) mixing the batch of step a) with at least one        pharmaceutically acceptable carrier if in step b) insoluble        matter is determined to be present below a predetermined amount.

In one embodiment of the process, if insoluble matter in the mixture ofstep b) is determined not to be present below a predetermined amount,the process further comprises:

-   -   d) dissolving the batch of step a) in water to form an aqueous        solution;    -   e) filtering the aqueous solution of step d) to reduce the        amount of insoluble matter to below the predetermined amount;    -   f) concentrating the aqueous solution of step e) to form a        concentrated solution;    -   g) adding a water-miscible anti-solvent to the concentrated        solution of step f) to form laquinimod sodium crystals; and    -   h) isolating the laquinimod sodium crystals of step g).

As used herein, a “pharmaceutically acceptable” component is one that issuitable for use with humans and/or animals without undue adverse sideeffects (such as toxicity, irritation, and allergic response)commensurate with a reasonable benefit/risk ratio.

Thus, a “pharmaceutically acceptable carrier” is a pharmaceuticallyacceptable solvent, suspending agent or vehicle, for delivering theinstant compounds to the animal or human. The carrier is selected withthe planned manner of administration in mind. Liposomes are also apharmaceutical carrier.

A dosage unit may comprise a single compound or mixtures of compoundsthereof. A dosage unit can be prepared for oral dosage forms, such astablets, capsules, pills, powders, and granules.

Drug substance can be administered in admixture with suitablepharmaceutical diluents, extenders, excipients, or carriers(collectively referred to herein as a pharmaceutically acceptablecarrier) suitably selected with respect to the intended form ofadministration and as consistent with conventional pharmaceuticalpractices. The unit will be in a form suitable for oral administration.The drug substance can be administered alone but are generally mixedwith a pharmaceutically acceptable carrier, and co-administered in theform of a tablet or capsule, liposome, or as an agglomerated powder.Examples of suitable solid carriers include lactose, sucrose, gelatinand agar. Capsule or tablets can be easily formulated and can be madeeasy to swallow or chew; other solid forms include granules, and bulkpowders. Tablets may contain suitable binders, lubricants, diluents,disintegrating agents, coloring agents, flavoring agents flow-inducingagents, and melting agents.

Specific examples of the techniques, pharmaceutically acceptablecarriers and excipients that may be used to formulate oral dosage formsof the present invention are described, e.g., in. U.S. PatentApplication Publication No. 2005/0192315. For instance, the oral dosageform of the present invention may comprise an alkaline-reactingcomponent, said component preferably amounting from about 1 to 20% byweight of the formulation in order to keep the pH above 8.

General techniques and compositions for making dosage forms useful inthe present invention are described-in the following references: 7Modern Pharmaceutics, Chapters 9 and 10 (Banker & Rhodes, Editors,1979); Pharmaceutical Dosage Forms: Tablets (Lieberman et al., 1981);Ansel, Introduction to Pharmaceutical Dosage Forms 2nd Edition (1976);Remington's Pharmaceutical Sciences, 17th ed. (Mack Publishing Company,Easton, Pa., 1985); Advances in Pharmaceutical Sciences (DavidGanderton, Trevor Jones, Eds., 1992); Advances in PharmaceuticalSciences Vol 7. (David Ganderton, Trevor Jones, James McGinity, Eds.,1995); Aqueous Polymeric Coatings for Pharmaceutical Dosage Forms (Drugsand the Pharmaceutical Sciences, Series 36 (James McGinity, Ed., 1989);Pharmaceutical Particulate Carriers: Therapeutic Applications: Drugs andthe Pharmaceutical Sciences, Vol 61 (Alain Rolland, Ed., 1993); DrugDelivery to the Gastrointestinal Tract (Ellis Horwood Books in theBiological Sciences. Series in Pharmaceutical Technology; J. G. Hardy,S. S. Davis, Clive G. Wilson, Eds.); Modern Pharmaceutics Drugs and thePharmaceutical Sciences, Vol 40 (Gilbert S. Banker, Christopher T.Rhodes, Eds.).

Tablets may contain suitable binders, lubricants, disintegrating agents,coloring agents, flavoring agents, flow-inducing agents, and meltingagents. For instance, for oral administration in the dosage unit form ofa tablet or capsule, the active drug component can be combined with anoral, non-toxic, pharmaceutically acceptable, inert carrier such aslactose, gelatin, agar, starch, sucrose, glucose, methyl cellulose,dicalcium phosphate, calcium sulfate, mannitol, sorbitol,microcrystalline cellulose and the like. Suitable binders includestarch, gelatin, natural sugars such as glucose or beta-lactose, cornstarch, natural and synthetic gums such as acacia, tragacanth, or sodiumalginate, povidone, carboxymethylcellulose, polyethylene glycol, waxes,and the like. Lubricants used in these dosage forms include sodiumoleate, sodium stearate, sodium benzoate, sodium acetate, sodiumchloride, stearic acid, sodium stearyl fumarate, talc and the like.Disintegrators include, without limitation, starch, methyl cellulose,agar, bentonite, xanthan gum, croscarmellose sodium, sodium starchglycolate and the like.

As used herein, an “anti-solvent” is a solvent in which laquinimodsodium is slightly soluble, very slightly soluble, practicallyinsoluble, or insoluble at room temperature (20-25° C.). The solubilityterms are defined below, in accordance with the United StatesPharmacopoeia XXV.

Parts of solvent required Term for 1 part solute Slightly soluble From100 to 1000 Very slightly soluble From 1000 to 10,000 Practicallyinsoluble 10,000 and over Insoluble 10,000 and over

As used herein, “density” is a measurement defined as the mass of asubstance per unit volume.

As used herein, “bulk density” or “BD” refers to a density measurementof a loose, uncompacted substance, wherein the volume of the substanceincludes the air trapped between particles.

As used herein, “tapped density” or “TD” refers to a density measurementof a substance that has been tapped or vibrated, thus minimizing thevolume of the substance by eliminating or minimizing the air trappedbetween particles.

The purification of impure crystalline compounds is usually attained byrecrystallization from a suitable solvent or mixture of solvents.(Vogel's Textbook of Practical Organic Chemistry. 5^(th) edition.Longman Scientific & Technical, 1989.) The recrystallization processgenerally comprises the following steps: a) dissolving the impurecrystalline substance in a suitable solvent near the boiling point; b)filtering the hot solution from particles of insoluble material anddust; c) allowing the hot solution to cool to cause the dissolvedsubstance to crystallize out and d) separating the crystals from thesupernatant solution. (Id.)

However, standard recrystallization techniques were accompanied by lowor no yields when applied to laquinimod sodium. As shown in Examples1-10, attempts to recrystallize laquinimod sodium resulted in pooryields, if any. The present invention provides an industriallyreproducible recrystallization process that results in high yields oflaquinimod sodium.

The process of the present invention uses an anti-solvent in whichlaquinimod sodium is practically insoluble. In addition, the process ofthe present invention concentrates the laquinimod sodium aqueoussolution before the addition of the anti-solvent.

The laquinimod sodium manufactured by the recrystallization processes ofthe present invention has increased purity over the laquinimod sodiumdisclosed in the prior art. U.S. Pat. No. 6,875,869 discloses a processof preparing the base compound laquinimod in high yield and low level ofimpurities. However, the process in U.S. Pat. No. 6,875,869 is only forsynthesis of the base compound and not the salt. As such, theslurry-to-slurry salt formation process would still be needed to formthe sodium salt. The slurry-to-slurry salt formation process previouslydisclosed is not efficient in removing any impurities present in thestarting material.

A second advantage of the recrystallization process of the presentinvention is environmentally-friendliness, as water is used as theprimary solvent.

A third advantage of the recrystallization process of the presentinvention is that laquinimod sodium crystals of a higher density thanthe laquinimod sodium crystals disclosed in the prior art are produced.Low tapped density is anathema to certain prized qualities in a drugsubstance such as compressibility, the ability of a powder to decreasein volume under pressure, and compactibility, the ability of a powder tobe compressed into a tablet of certain strength or hardness. Crystalswith low tapped density are also known to have poor flowability, whichresults in a lack of uniformity of content in finished dosage forms,especially in tablets. (Rudnic et al. Chpt. 45, Remington'sPharmaceutical Sciences, 20^(th) Edition, Lippincott Williams & Wilkins,Baltimore, Md. (2000)) Problems of uniformity of content are especiallyimportant in tablets in which the amount of active pharmaceuticalingredient within the tablet is low.

A fourth advantage of the recrystallization process of the presentinvention is that the resulting laquinimod sodium crystals haveincreased particle size. Larger particles of laquinimod sodium are moreprocessable when making pharmaceutical compositions. Smaller particlesare often associated with dust-like properties which may interfere withprocessing in manufacture of pharmaceutical compositions. In addition,smaller particles are sometimes associated with flowability problemswhich may interfere with the manufacture of pharmaceutical compositions.Furthermore, in some instances, chemical stability has been shown to bedecreased by the increase in surface area that results from smallerparticle size. (Felmeister, A. Chpt 88, Remington's PharmaceuticalSciences, 15^(th) Edition, Mack Publishing Company, Easton, Pa. (1975)).

EXPERIMENTAL DETAILS

Determination of Powder Density

Bulk Density

-   -   1. Mix powder;    -   2. Tare a 50 ml empty cylinder on a 0.01 g sensitivity balance;    -   3. Transfer the powder, without compacting, to the cylinder        being held at approximately a 45 degree angle to achieve an        untapped apparent volume of 40 to 50 ml.    -   4, Bring the cylinder containing the sample to a vertical        position by a sharp move in order to level the volume for        reading.    -   5. Read the apparent volume (Va) to the nearest graduated unit;    -   6. Weigh the cylinder with sample (the balance gives sample        weight M);    -   7. Calculate bulk density in g/ml according to the following        equation: BD=M/Va;    -   8. Perform steps 1-7 again and report the average data of        duplicates.

Tapped Density

-   -   1. Put the same cylinder used to calculate Bulk Density in a        Quantachrome Dual Autotap instrument;    -   2. Perform 1250 taps;    -   3. Read the tapped volume (Vf) to the nearest graduated unit;    -   4. Calculate the tapped density in g/ml according to the        following equation: TD=M/Vf;    -   5. Perform steps 1-4 again and report the average data of        duplicates.

Determination of Particle Size

The particle size distributions were measured by Malvern LaserDiffraction, using the Mastersizer S model. Laser diffraction relies onthe fact that diffraction angle of light is inversely proportional toparticle size. Properties of particles are measured and interpreted asmeasurements of a sphere (a sphere being the only shape that can bedescribed by one unique number). In addition, laser diffractioncalculates a particle size distribution based around volume terms, thuseliminating particle count from the determination of particle size. TheMastersizer S model measures particles using a single technique and asingle range setting.

D(0.1) is the particle size, in microns, below which 10% by volumedistribution of the population is found. D(0.5) is the particle size, inmicrons, below which 50% by volume distribution of the population isfound. D(0.9) is the particle size, in microns, below which 90% byvolume distribution of the population is found.

Determination of Heavy Metals

Metal content was measured using inductively coupled plasma atomicemission spectrometry using an inductively coupled plasma atomicemission spectrometry (“ICP-AES”) system manufactured by Spectro (Kleve,Germany). Sample digestion was performed in 65% nitric acid, and theinternal standard used was scandium.

Note: In the following examples the volumes of solvents used arecalculated relative to starting weight of laquinimod sodium. The yieldsare calculated in weight percent.

Determination of Purity

Laquinimod sodium and polar impurity/degradation products weredetermined by isocratic reversed phase high performance liquidchromatography (RP-HPLC), using an ODS-3V column and a mobile phasecomprised of a mixture of ammonium acetate buffer at pH 7.0 (80%) andacetonitrile (20%). The detection technique was ultraviolet absorptionat 240 nm.

EXAMPLE 1 Method of Preparing Laquinimod Sodium

Laquinimod acid was prepared according to the method described in U.S.Pat. No. 6,875,869:5-Chloro-1,2-dihydro-4-hydroxy-1-methyl-2-oxo-quinoline-3-carboxylicacid methyl ester (3.0 g), N-ethylaniline (2 eq 2-2.88 ml), and heptane(60 ml) were heated and the volatiles, mainly heptane and formedmethanol, (32 ml) distilled off during 6 hours and 35 minutes. Aftercooling to room temperature the crystalline suspension was filtered andthe crystals were washed with heptane and dried in vacuum to yieldlaquinimod acid (3.94 g, 98%) as white to off-white crystals.

Laquinimod acid was converted into laquinimod sodium using the methoddescribed in U.S. Pat. No. 6,077,851, Example 2: A solution of 5 Msodium hydroxide was prepared by dilution of a 50% by weight sodiumhydroxide solution (10.0 g) with sterile water to the total volume of 25ml.N-Ethyl-N-phenyl-1,2-dihydro-4-hydroxy-5-chloro-1-methyl-2-oxo-quinoline-3-carboxamide(10.0 g) was suspended in ethanol (150 ml) and the previously prepared 5M sodium hydroxide solution was added to pH of 8-12 (5.6 ml). Thereaction mixture was stirred for another 30 minutes at ambienttemperature. The resulting precipitation was filtered off and rapidlywashed twice with ethanol (2×150 ml). The precipitate was then dried invacuum over P₂O₅ to give the title compound (9.5 g), yield 90%. Thisprocess is known as a “slurry-to-slurry process.”

EXAMPLE 2

Laquinimod sodium prepared according to Example 1 was added to 6.1volumes of water at 50° C. The pH was adjusted to 12.5 by the additionof NaOH and the mixture was stirred until complete dissolution. 50.0volumes of ethanol were added. The solution was cooled to 2° C. but nocrystallization occurred.

EXAMPLE 3

Laquinimod sodium prepared according to Example 1 was added to 6.1volumes of water at 50° C. The pH was adjusted to 12.5 by the additionof NaOH and the mixture was stirred until complete dissolution. 100.0volumes of ethanol were added. The solution was cooled to −18° C. but nocrystallization occurred.

EXAMPLE 4

Laquinimod sodium prepared according to Example 1 was added to 6.1volumes of water at 50° C. The pH was adjusted to 12.5 by the additionof NaOH and the mixture was stirred until complete dissolution. 50.0volumes of ethanol were added. The solution was cooled to −18° C. but nocrystallization occurred.

EXAMPLE 5

Laquinimod sodium prepared according to Example 1 was added to 6.1volumes of water at 50° C. The pH was adjusted to 12.5 by the additionof NaOH and the mixture was stirred until complete dissolution. 50.0volumes of ethanol were added. The solution was acidified to a pH of 5.0by the addition of HCl. The solution was cooled to 4° C., andcrystallization occurred. The compound which crystallized was filteredand washed with 20 mL of ethanol: water solution 1:1 and was dried at50° C. under vacuum to a constant weight and was determined to belaquinimod acid, in a yield of 56.2%.

Discussion of a Examples 2-5

In Examples 2-5, recrystallization was attempted by dissolving thelaquinimod sodium in a small amount of water and by addition of ethanolas an anti-solvent. Although the solubility of laquinimod sodium inethanol is low (laquinimod sodium is slightly soluble in ethanol at roomtemperature), nevertheless, no crystallization of laquinimod sodium wasattained even though large quantities (as much as 100 volumes) ofethanol were added.

EXAMPLE 6

Laquinimod sodium prepared according to Example 1 was added to 9.9volumes of water at 76° C. The pH was adjusted to 10.5-11 by theaddition of NaOH and the mixture was stirred until complete dissolution.The solution was cooled to 3° C. but no crystallization occurred.

EXAMPLE 7

Laquinimod sodium prepared according to Example 1 was added to 9.9volumes of water at 76° C. The pH was adjusted to 10.5-11 by theaddition of NaOH and the mixture was stirred until complete dissolution.30.6 volumes of isopropanol were added. The solution was cooled to 5° C.but no crystallization occurred.

Discussion of Examples 2-7

Example 6 shows that merely cooling an aqueous solution of laquinimodsodium does not cause crystallization. Example 7 shows that addition ofisopropanol anti-solvent (laquinimod sodium is very slightly soluble inisopropanol at room temperature) to an aqueous solution of laquinimodsodium does not cause crystallization.

Examples 2-7 show that standard methods of recrystallization were noteffective when used for recrystallization of laquinimod, as either nocrystallization occurred or low yields were attained.

EXAMPLE 8

The solution of Example 7 was then concentrated by evaporation undervacuum to 3.8 volumes. A small amount of solid crystallized out ofsolution. The mixture was cooled at 7° C. overnight. The mixture wasfiltered, and the solid crystals were washed with 20 ml of isopropanoland were dried at 50° C. under vacuum to a constant weight. The yieldwas determined to be 11.2%.

EXAMPLE 9

The filtrate from Example 8 was collected, and 8.2 volumes (relative tostarting laquinimod sodium in Example 7) isopropanol were added to thefiltrate at room temperature. The filtrate with isopropanol was thencooled to 7° C., and a solid crystallized out of solution. The crystalswere washed with 10 ml of isopropanol and were dried at 50° C. undervacuum to a constant weight and the yield was determined to be 29.8% (ofstarting laquinimod sodium of Example 7.)

EXAMPLE 10

Laquinimod sodium prepared according to Example 1 was added to 9.9volumes of water at 76° C. The pH was adjusted to 10.5-11 by theaddition of NaOH and the mixture was stirred until complete dissolution.91 volumes of acetone were added. The solution was cooled to 5° C. and acrystallization of a small amount of solid was noticed. The solid waswashed with acetone and filtered and dried at 50° C. under vacuum to aconstant weight. The yield was determined to be 10.2%.

EXAMPLE 11

Laquinimod sodium prepared according to Example 1 was added to 9.9volumes of water at 76° C. The pH was adjusted to 10.5-11 by theaddition of NaOH and the mixture was stirred until complete dissolution.The solution was concentrated to 1.4 volumes using a rotationevaporator.

8.0 volumes of acetone were added to the solution, and crystallizationoccurred. The mixture was cooled to 7° C. overnight. The solid wasfiltered and dried at 50° C. under vacuum to a constant weight. Thesolid was determined to be laquinimod sodium, with a yield of 90.3%.

Discussion of Examples 10 and 11

Example 10 shows that addition of even large amounts of acetone(laquinimod sodium is practically insoluble in acetone at roomtemperature) to a non-concentrated aqueous solution of laquinimod sodiumprovides low yields of crystalline laquinimod sodium.

On the other hand, Example 11 shows that if laquinimod sodium aqueoussolution is first concentrated, and then anti-solvent is added, theyields of laquinimod sodium crystal are high. Large amounts ofanti-solvent are not required to attain high yields in this case.

EXAMPLE 12

Laquinimod sodium prepared according to Example 1 was added to 11.1volumes of water at 78° C. The pH was adjusted to 12 by the addition ofNaOH and the mixture was stirred until complete dissolution. Thesolution was concentrated to 1.9 volumes using a rotary evaporator. Thesolution was transferred to a warmed reactor (jacket temperature 50° C.)

9.5 volumes of acetone were slowly added to the solution, andcrystallization occurred. The mixture was cooled to 3° C. and mixed for1.5 hours in the reactor. The solid was filtered and washed with freshacetone, and dried at 50° C. under vacuum to a constant weight and wasdetermined to be laquinimod sodium, with a yield of 79.5%.

EXAMPLE 13 Recrystallization without Seeding

46.7 g of laquinimod sodium prepared by a scaled-up process followingthe procedure of Example 1 (batch A), and 500 ml of deionized water wereintroduced into a laboratory glass reactor. The mixture was stirred andheated to 50° C. until complete dissolution of the solids was observed.The solution was filtered through filter paper, and the filter waswashed with 10 ml of water and the wash was combined with the filtrate.

The resulting solution was introduced into a laboratory reactor equippedwith a vacuum distillation system. The solution was concentrated byevaporation under vacuum (35-38 mbar) to a volume of 112 ml. Afterevaporation, the pressure was adjusted to atmospheric pressure and thejacket temperature was raised to 50° C., and 295 g of acetone were addedto the batch over 2 hours. Solid crystallization was observed during theacetone addition. The batch was cooled to 2° C. and stirred at thistemperature for 12 hours. The solid product was isolated by filtration,washed twice with acetone and dried under vacuum at 35-40° C. toconstant weight. 35.7 g of dry solid was obtained, yield 76.4%.

The starting material prepared according to Example 1 (batch A) and thedry recrystallized product were sampled and analyzed for particle sizedistribution, powder density and chemical purity. The results arepresented in Table 1:

TABLE 1 Properties and purity of laquinimod sodium, Example 13Laquinimod Sodium prepared according Re- to Example 1 crystallizedQuality parameters (batch A) product Particle size d(0.1) 1.5 13.3distribution by d(0.5) 7.1 51.1 Malvern, micron d(0.9) 23.2 105.1 Powderdensity, BD 0.166 0.498 g/ml TD 0.347 0.758 Heavy metals by Fe 7 <2 ICP,ppm Ni 0.6 <0.5 Cr 0.7 0.3 Color Grey Off-white Purity by HPLC, Impurity1, 0.06 Not area % RT = 5.49 detectable HPLC = High Performance LiquidChromatography RT = Retention Time

The method of Example 13 was accompanied by high yields which areindustrially reproducible.

Example 13 shows that the recrystallization process increased the purityof the laquinimod sodium, as the impurity peak 1 was no longerdetectable after recrystallization, and the color was changed. Inaddition, the content of heavy metals Fe, Ni, and Cr was decreased.

In addition, the powder density of the laquinimod sodium was increased,and the size of the particles was also increased.

EXAMPLE 14 Laquinimod Sodium Recrystallization with SpontaneousCrystallization—Nucleation in Water

71.4 g of laquinimod sodium prepared by a scaled-up process followingthe procedure of Example 1 (batch B) and 750 ml deionized water wereintroduced into a laboratory glass reactor. The mixture was stirred andheated to 60° C., and complete dissolution of the solids was observed.The solution was filtered through filter paper, the filter was washedwith 36 ml water and the wash was combined with the filtrate.

The resulting solution was introduced into a laboratory reactor equippedwith a vacuum distillation system. The batch was concentrated byevaporation under vacuum (37-38 mbar) to a volume of 153 ml. After theevaporation completion, the reactor pressure was adjusted to atmosphericpressure and the jacket temperature was adjusted to 50° C. The batch wasstirred for 25 minutes. At this stage spontaneous crystallization ofsolids was observed. Then 450.5 g acetone was added to the batch over 2hours. The batch was cooled to 2° C. and stirred at this temperature for12 hrs, then the solid product was isolated by filtration, washed twicewith acetone and dried under vacuum at 35-40° C. to a constant weight.64.2 g of dry solid was obtained, yield 89.9%.

The starting material prepared according to Example 1 (batch B) and thedry, recrystallized product were sampled and analyzed for particle sizedistribution, powder density and chemical purity. The results arepresented in Table 2:

TABLE 2 Properties and purity of Laquinimod Sodium, Example 14Laquinimod Sodium prepared according Re- to Example 1 crystallizedQuality parameters (batch B) product Particle size d(0.1) 2.1 3.5distribution by d(0.5) 10.8 15.7 Malvern, micron d(0.9) 35.3 43.2 Powderdensity, BD 0.189 0.224 g/ml TD 0.452 0.429 Heavy metals by Fe 4 <2 ICP,ppm Ni <0.5 <0.2 Cr 1 0.2 Color White White Purity by HPLC, Impurity 1,0.03 0.00 area % RT = 5.52 Impurity 2, 0.05 0.01 RT = 8.48 Impurity 3,0.03 0.00 RT = 12.19

EXAMPLE 15 Recrystallization Method with SeededCrystallization—Controlled Nucleation in Water

25.0 g of laquinimod sodium prepared by a scaled-up process followingthe procedure of Example 1 (batch C) and 260 ml of deionized water wereintroduced into a laboratory glass reactor. The mixture was stirred andheated to 60° C., and complete dissolution of the solids was observed.The solution was filtered through filter paper, the filter was washedwith 15 ml of water and the wash was combined with the filtrate. Theresulting solution was concentrated by evaporation in a rotationevaporator under vacuum (20-25 mbar) to a residual weight of 60.0 g.After the evaporation completion, the residue was introduced into alaboratory glass reactor which was pre-heated to 50° C. (jackettemperature). The batch was seeded with 0.2 g of solid laquinimod sodiumand stirred for one hour, and crystallization of solids was observed.Then 157.7 g of acetone were added to the batch over 2 hours. The batchwas cooled to 2° C. and stirred for 12 hours. The solid product wasisolated by filtration, washed twice with acetone, and dried undervacuum at 35-40° C. to a constant weight. 22.6 g of dry solid wasobtained, yield 90.4%.

The starting material prepared according to Example 1 (batch C) and thedry, recrystallized product were sampled and analyzed for particle sizedistribution, powder density and chemical purity. The results arepresented in Table 3;

TABLE 3 Properties and purity of Laquinimod Sodium Laquinimod Sodiumprepared according Re- to Example 1 crystallized Quality parameters(batch C) product Particle size d(0.1) 1.3 6.1 distribution by d(0.5)5.9 21.2 Malvern, micron d(0.9) 19.4 51.8 Powder density, BD 0.158 Nodata g/ml TD 0.362 No data Heavy metals by Fe 25 8 ICP, ppm Ni 2.9 1.1Cr 3.5 1.5 Color Grey Off-white Purity by HPLC, Impurity 1, 0.02 Notarea % RT = 5.49 detectable Impurity 2, 0.03 Not RT = 8.38 detectable

Discussion of Examples 14 and 15

The methods of Examples 14 and 15 were accompanied by high yields whichare industrially reproducible.

Examples 14 and 15 show that the recrystallization process increased thepurity of the laquinimod sodium, as the impurity peaks were no longerdetectable after recrystallization. In addition, the content of heavymetals Fe, Ni, and Cr was decreased. The crystals which resulted afterrecrystallization in examples 14 and 15 were larger than the crystalsbefore the recrystallization.

EXAMPLE 16 Crystallization without Seeding—Nucleation in the Presence ofAcetone

Water (532 mL) and laquinimod sodium (52.3 g) were introduced into alaboratory glass reactor (0.5 L). The suspension was heated to 70-73° C.until a clear solution was obtained. The hot solution was cooled to 50°C. and then filtered through a 0.2 micron filter. The filter was washedwith 10 ml of water and the wash was combined with the filtrate. Theresulting solution was concentrated to a volume of 112 mL in a 1 literreactor by evaporation while stirring under a vacuum of 30-50 mbar whilemaintaining the jacket temperature at 60° C., and the temperature of thereactor at about 35-40° C. Immediately after the evaporation completionand adjustment of pressure, acetone (417 mL) was added to theevaporation residue over 2 hours while the jacket temperature wasmaintained at 50° C. The crystallization mixture was cooled to atemperature of 2° C. over 2 hours and was kept at this temperature for5-10 hours. The solid formed was collected by filtration and washedtwice with 50 mL of acetone. The wet material was dried in a dryer at30-40° C. under vacuum to give 47.6 gram (90.6% yield) of driedmaterial. The results are presented in Table 4:

TABLE 4 Properties of Laquinimod Sodium, Example 16 Laquinimod Sodiumaccording to Re- Example 1 crystallized Quality parameters (batch B)product Particle size d(0.1)  2.1 15.7 distribution by d(0.5) 10.8 65.5Malvern, micron d(0.9) 35.3 156.4  Color White White

The crystals produced by the recrystallization process were larger thanthe crystals of the starting material.

EXAMPLE 17 Recrystallization of Crude Laquinimod Sodium with InsolubleImpurities

A 55 mg sample of laquinimod sodium prepared by a scaled-up processfollowing the procedure of Example 1 (batch D) was mixed in 0.5 mL ofdeionized water at ambient temperature. The sample did not completelydissolve in water.

Purification by recrystallization of a sample of the batch was performedas follows:

Water (391 mL) and laquinimod sodium of Example 1 (batch D) (39.1 g)were introduced into a laboratory glass reactor (0.5 L). The suspensionwas heated by raising the jacket temperature to 73° C. After 20 min thesolution was not clear. The suspension was warmed further by raising thejacket temperature to 75° C. and a clear solution was still notobtained. The hot solution was cooled to 50° C. and filtered throughlaboratory filter paper over a Buchner funnel. 0.3 grams of solidresidue remained on the filter paper. A sample of the solid residue wastested for impurity content. The filter papers were washed with 47 ml ofwater and the wash was combined with the filtrate. The resultingsolution was cooled by lowering the jacket temperature to 25° C. and thesolution was then concentrated under vacuum (P<45 mmHg) while heatingover the course of 30 min by raising the jacket temperature to 65° C.After completion of, evaporation, the residue (82.1 ml, 93.2 g, d=1.135g/ml) was cooled by lowering the jacket temperature to 50° C. andagitated for 10 min. The batch was then seeded with solid laquinimodsodium and was stirred while maintaining the jacket temperature at 50°C. for 1 hour. Acetone (316.7 mL, 250.2 g) was then added to thecrystallizing mixture over 2 hours at 50° C. The resulting suspensionwas cooled to 2° C. over 4 hours and kept at this temperature foranother 11 hours. The solid formed was collected by filtration and waswashed twice with 31.3 g of acetone. The wet material was dried in adryer at 30-40° C. under vacuum to yield 31.7 gram (81.1%) of driedcrystalline laquinimod sodium. The impurity content of the crudelaquinimod sodium was tested by ICP before and after recrystallization.

TABLE 5 Impurity content in PPM of Laquinimod Sodium Laquinimod Sodiumprepared according Re- to Example 1 crystallized Solid Impurity (batchD) product Residue Al 14.0 5.6 411 Ca 165 65 860 Cr 2.6 <0.5 99 Cu 2.81.3 64 Fe 31.5 5.8 1544 Ni 5.5 <0.5 69 S 466 <1 193 Zn 20.5 7.5 352

Discussion of Example 17

Even though crude laquinimod sodium had high insoluble impurity levelsbefore recrystallization, the recrystallization process had lowered theimpurity levels. The high impurity content in the solid residue showsthe importance of filtration of aqueous laquinimod solution in order tolower levels of impurities. Thus it is desirable to lower the amount ofinsoluble matter to below an amount that has been predetermined to causedeleterious effects on, e.g., stability of the laquinimod formulation.

1. A mixture of crystalline laquinimod sodium particles, wherein 10% ormore of the total amount by volume of the laquinimod sodium particleshave a size of greater than 40 microns. 2.-40. (canceled)